Chemistry of thienopyridines. VIII. Substitution products derived from thieno[2,3‐ b ] pyridine 7‐oxide

Thieno[2,3‐ b ]pyridine (I) was concerted to the N ‐oxide (II, 53%) by means of hydrogen peroxide and acetic acid. Nitration of II in sulfuric acid gave 4‐nitrothieno[2,3‐ b ]pyridine 7‐oxide (III, 50%), while nitration in acetic acid formed the isomeric 5‐nitrothieno[2,3‐ b ]pyridine 7‐oxide (IV, 54%). Compounds III and IV were reduced to the corresponding 4‐ and 5‐aminothieno[2,3‐ b ]pyridines, respectively. Treatment of III with acetyl chloride gave 4‐chlorothieno‐[2,3‐ b ]pyridine 7‐oxide (XI, 81%), convertible in two steps to 4‐( N ‐substituted amino)thieno‐[2,3‐ b ]pyridines (especially of the 4‐dialkylaminoalkylamino type) for screening as potential antimalarial drugs. 4‐Aminothieno[2,3‐ b ]pyridine reacted with aromatic aldehydes to give Schiff's bases and other products. Mechanisms for some of the reactions are suggested. NMR spectral data are reported for various 4‐substituted thieno[2,3‐ b ]pyridine compounds.